Multilevel Hierarchical Modeling of
Benthic Macroinvertebrate Responses to
Urbanization in Nine Metropolitan Regions
across the Conterminous United States

ABSTRACT

Multilevel hierarchical modeling methodology has been
developed for use in ecological data analysis. The effect
of urbanization on stream macroinvertebrate communities
was measured across a gradient of basins in each of nine
metropolitan regions across the conterminous United States.
The hierarchical nature of this dataset was harnessed in a
multi-tiered model structure, predicting both invertebrate
response at the basin scale and differences in invertebrate
response at the region scale. Ordination site scores, total taxa
richness, Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa
richness, and richness-weighted mean tolerance of organisms
at a site were used to describe invertebrate responses. Percentage
of urban land cover was used as a basin-level predictor
variable. Regional mean precipitation, air temperature, and
antecedent agriculture were used as region-level predictor
variables. Multilevel hierarchical models were fit to both
levels of data simultaneously, borrowing statistical strength
from the complete dataset to reduce uncertainty in regional
coefficient estimates. Additionally, whereas non-hierarchical
regressions were only able to show differing relations between
invertebrate responses and urban intensity separately for each
region, the multilevel hierarchical regressions were able to
explain and quantify those differences within a single model.
In this way, this modeling approach directly establishes the
importance of antecedent agricultural conditions in masking
the response of invertebrates to urbanization in metropolitan
regions such as Milwaukee–Green Bay, Wisconsin; Denver,
Colorado; and Dallas–Fort Worth, Texas. Also, these models
show that regions with high precipitation, such as Atlanta,
Georgia; Birmingham, Alabama; and Portland, Oregon,
start out with better regional background conditions of
invertebrates prior to urbanization but experience faster
negative rates of change with urbanization. Ultimately, this
urbanization-invertebrate response example is used to detail
the multilevel hierarchical construction methodology, showing
how the result is a set of models that are both statistically more
rigorous and ecologically more interpretable than simple linear
regression models.